The invention relates to a bogie, particularly for a railway vehicle, intended to support a load such as the body of the vehicle or a power plant, resting on a number of wheels divided between axles.
Given the mass supported and the speed of travel, the forces due to accelerations, particularly during changes of direction, are high and this is why it is commonplace to produce bogies in the form of solid steel components or mechanical/welded structures. These components and these structures are heavy (generally between 1300 and 1900 kg) and rigid and have to be equipped with suspension and damping systems in order to safeguard the comfort of the passengers of the vehicle and absorb vibrations due to the unevennesses of the railway track on which the vehicle runs; this means that, given the permissible axle loads, the load which can be carried in the body is, of necessity, particularly restricted.
European Patent Application 0,031,008 discloses a railway vehicle bogie comprising chassis parts in the shape of an H made of composite material; these chassis parts do not allow either the effective absorption of the forces due to vertical and transverse accelerations of the moving parts, or the mounting of accessories or safety equipment such as an engine, a braking system or a control system, because in order to effectively withstand the dynamic stresses generated, they would have to have a large cross section and this would take a significant amount of composite material, increasing the cost of the bogies and posing technical problems with moulding; furthermore, with this design, it is difficult to obtain a chassis which has flexibility properties that are identical on each side of the longitudinal mid-plane of the bogie.
The object of the invention is to overcome these drawbacks and to create a bogie which has a structure such that the side members play an effective part in the vehicle suspension while at the same time retaining a simple geometry and an attractive cost improving the overall economic performance of the bogie.
To this end, the invention relates to a bogie designed to be secured so that it rests on wheels and comprising at least two wheel axles, at least one side member extending from the axles to an at least approximately central part of the length of the bogie, and axle boxes in which the axles are mounted so that they can rotate, the bogie being characterized in that the side member comprises at least one interchangeable elastic leaf constituting parametrizable primary suspension, made of composite material based on fibres embedded in a resin, and a region of each end of the side member is housed in a side-member sleeve resting on a respective axle box via at least one insert element.
For example and as a preference, the side member consists of a single leaf which, being elastic and interchangeable, constitutes parametrizable primary suspension and is made of composite material.
By virtue of these characteristics, the side member which, simultaneously, fulfils functions of supporting the vehicle between the axles, acting as primary suspension for the vehicle, damping vibrations between the axles and the vehicle, and providing the axles with lateral guidance, plays a part in lightening the bogie compared with conventional steel structures, and this makes it possible to increase the load carried in the vehicle. The flexibility of the composite material, for example based on glass, carbon or aramid fibres, embedded in an epoxy or some other resin, allows it to perform effective damping at the vibrational frequencies most often excited in a bogie. Furthermore, the geometry of the side member may be chosen to be such that this member is simple to manufacture. The insert piece, which can move longitudinally with respect to the side member sleeve and the axle box, makes it possible to absorb differences associated with the vehicle loading and to damp the bogie pitching phenomenon.
According to a preferred feature of the invention, the insert element is a damping means made at least partially of elastomer, for example of rubber, and preferably of elastomer-metal, which is stressed as a function of the elastic deformations of the elastic side member leaf and, together with the latter, makes it possible to damp the movements of the bogie.
According to another advantageous feature of the invention, the damping insert element constitutes an additional primary suspension stage for parametrizing the rigidity of the suspension.
According to another feature, as an alternative, the insert element is a component, for example made of metal, rubbing against a side friction block by way of damping element, and this makes it possible for a bogie to be fitted out at a more attractive cost when there is no need to optimize the effectiveness of the suspension.
According to yet another optional feature of the invention, the bogie has two side members each comprising at least one elastic leaf which is preferably monolithic, these leaves being connected to the one same bogie transom; it is possible to contrive for each side member to be connected to the transom underneath this transom at the upper part of the central region of the length of the leaf, and this allows this transom to support the vehicle while at the same time being equipped with secondary suspension means.